The present invention generally relates to a fluorescence emitting device using a phosphor emitting a light by an electron bombardment, and more particularly to an electron beam excited fluorescence emitting device having an excellent luminance lifetime, and driving at a driving anode voltage of 50V and above.
Conventionally, in a field emission display (hereinafter referred to as “FED”) using a field emission cathode and a vacuum fluorescent display (hereinafter referred to as “VFD”), various kinds of phosphors has been used in order to obtain luminescent colors. A blue light emitting phosphor for use in a display excited by an electron beam bombardment is generally known in the Japanese Patent Publication No. 2003-55657 and the Japanese Patent Publication No. 2004-285363. The Japanese Patent Publication No. 2003-55657 discloses a low-velocity electron beam excited (Y, Ce)2 O3.SiO2 phosphor emitting a blue light having the composition formula[(Y, Ce)2O3.nSiO2(wherein 0.4≦n≦1.0)]. The Japanese Patent Publication No. 2004-285363 discloses ZnS:Ag, and Al, ZnS:Ag phosphor powders emitting a blue light which has less crystal defect and minimal degradation compared to conventional phosphor powders, if it is used for a long period of time. The phosphor disclosed in the Japanese Patent Publication No. 2004-285363 is effective for maintaining luminance of the phosphor, and to improve reliability or lifetime performance of a cold cathode field emission display.
On the other hand, a conventional phosphor is irradiated with an exciting source such as a light or electron beam having a high energy to emit a light. As a result, it has been a problem that the luminance of the phosphor is degraded due to the excitation of high energy. Accordingly, a phosphor exhibiting less luminance degradation is required. In order to provide a phosphor that complies with such a requirement, the Japanese Patent Publication No. 2004-277663 discloses α-type sialon phosphors emitting a blue light having a general formula [(Si, Al)12(O, N)16]. The Japanese Patent Publication No. 2005-8794 discloses α-type sialon phosphors illustrated by the composition formula Ca0.25 Ce0.25[(Si, Al)12(O, N)16].
It is to be noted that the Y2 SiO5: Ce phosphor disclosed in the Japanese Patent Publication No. 2003-55657 exhibits a remarkable decrease in luminous efficiency during its lifetime, and there is an extreme difference in the degree of degradation in RGB (red, green and blue), particularly “blue”, when it is used for FED. Furthermore, the lifetime of a device incorporating the phosphor is short and loses color balance. In an FED excited at a driving voltage of approximately 3 kV, a metal is unlikely to be used due to the penetration depth of an electron.
The ZnS: Ag, Al phosphor containing sulfur as ZnS: Ag, Al disclosed in the Japanese Patent Publication No. 2004-285363 does not provide a satisfactory emission performance and device lifetime, because sulfur scatters by electron bombardment and contaminates the electron source.
In the sialon phosphor disclosed in the Japanese Patent Publications No. 2004-277663 and No. 2005-8794, there is no disclosure as to how the sialon phosphor is applied to a fluorescent emission device such as a field emission device and the like.